Do not assume that all presubmit directories still exist.

presubmit_support.py

Index: presubmit_support.py
diff --git a/presubmit_support.py b/presubmit_support.py
index 2922b4e32938c873da53decfc4e646e9b8d73174..84a1f9bcff27a9d07cfc4006688dae4e4c050b90 100755
--- a/presubmit_support.py
+++ b/presubmit_support.py
@@ -1093,11 +1093,14 @@ def ListRelevantPresubmitFiles(files, root):
   # Look for PRESUBMIT.py in all candidate directories.
   results = []
   for directory in sorted(list(candidates)):
-    for f in os.listdir(directory):
-      p = os.path.join(directory, f)
-      if os.path.isfile(p) and re.match(
-          r'PRESUBMIT.*\.py$', f) and not f.startswith('PRESUBMIT_test'):
-        results.append(p)
+    try:
+      for f in os.listdir(directory):

[tandrii(chromium), 2016/08/17 10:01:56]

the only thing that can raise here is this line, so I don't see a reason to wrap
everything in try-catch. In fact, you could do which is even better:

if not os.path.isdir(directory):
  continue
for f in os.listdir......
  ...

+        p = os.path.join(directory, f)
+        if os.path.isfile(p) and re.match(
+            r'PRESUBMIT.*\.py$', f) and not f.startswith('PRESUBMIT_test'):
+          results.append(p)
+    except OSError:
+      pass
 
   logging.debug('Presubmit files: %s', ','.join(results))
   return results